Continuous, subjective sonographic grayscale analysis of uterine involution in sows during the postpartum period

Objective The aim of this study was to analyse the continuous and subjective evaluation of echogenicity, echotexture of the puerperal uterus as well as the presence of intrauterine fluid in sows of differing parity stages. The goal was to determine associations between grayscale values and simultaneously assessed uterine diameter, body condition, and additional performance parameters such as farrowing duration, placenta expulsion duration, placenta weight and litter weight. Material and methods The study population included 95 sows housed either in free farrowing (n = 46) or crated (n = 49) stables. Transabdominal ultrasound was performed daily between postpartum days 2-14 (p.p.) and the day before weaning. Echogenicity (ranging between anechoic (1)-hyperechoic (6)), echotexture (homogenous/heterogeneous), and the presence of intrauterine fluid (yes/no) was evaluated on three cross-sections of the uterine horn/sow/day. Results In the first week p.p, most sows showed a medium (median = 4.0) echogenicity, whereas from day 7 p.p., echogenicity decreased (median = 3.5 to 3.0). Echotexture between days 2-7 p.p was mainly heterogeneous, whereas between days 8-14 p.p, it proved to be mostly homogeneous. Intrauterine fluid was detected until day 9. Echogenicity exhibited significant association with farrowing duration (FD) on days 8-14 p.p. (p = 0.048). Sows with FD > 300 min showed slightly lower echogenicity (median = 3.0) than sows with FD <= 300 min (median = 3.5). There was a positive correlation between uterine diameter and echogenicity on day 2-7 p. p. (r = 0,359, p < 0.001) and days 8-14 p. p. (r = 0,381, p < 0.001). Conclusions Subjective grayscale analysis by ultrasonography is suitable in characterizing uterine echogenicity and echotexture as well as intrauterine fluid in post-partum sows. The presented findings suggest that this may aide in assessing patterns of the sow's puerperium.